This invention relates to an electron beam exposure apparatus.
An electron beam exposure apparatus is used as shown in FIG. 1 in the prior art to form a pattern on a semiconductor wafer or a photo-mask. To form a pattern on, for example, an electron sensitive photo-mask 112, the mask is put on an X-Y stage (not shown) which is placed opposite to an electron gun 114. Electron gun 114 emits an electron beam 116, which scans the pattern area 110 of photo-mask 112. The electron beam passes through blanking electrodes (not shown) and deflection electrodes 118 which govern the intensity and position of the beam. These electrodes are controlled by exposure pattern data to assure that the correct pattern is placed on the photo-mask.
The electron beam 116 may be moved a limited maximum distance W in a first direction (X direction) by operation of deflection electrodes 118. This first direction may be referred to as the "scanning" direction. The photo-mask 112 may be moved in a second direction (Y-direction) perpendicular to the scanning direction. The scanning distance W is typically shorter than the X-direction width of photo-mask 112. Accordingly, a narrow stripe 120 is formed which is equal in width to the maximum scanning distance W. During such a scan, the intensity of the electron beam is controlled by the exposure pattern data. Furthermore, upon finishing the scanning of a stripe area 120 of the mask, the mask is shifted in the scanning direction (X-direction) so that the electron beam may scan a next stripe area 122. This process continues until the entire pattern area 110 is scanned.
Known electron beam exposure apparatus are used to form a pattern on the mask in the following manner. The surface of the mask is divided into a plurality of stripe areas, for example stripe areas 120, 122, 124, 126 and 128. Each stripe area has a width of W, which for example, may be 256 um, the largest width over which the electron beam can scan with permissive distortion when deflected by deflection electrodes 118. Each stripe area may be further divided along its length into cells. For example, in FIG. 1, stripe area 124 is shown being divided into four cells, each having a Y-direction length "a" equal to 256 um to form square cells of 256 um.times.256 um. Each cell in a stripe area is sequentially exposed to the electron beam.
Therefore, to form a pattern on the mask by the known apparatus it is necessary to have data available which represents the content of each of the 256 um.times.256 um cells. Such data is obtained by analyzing the pattern content in each cell. As mentioned above, the X-direction width of each cell is determined by the longest distance over which the electron beam can scan with permissive distortion. Thus, even if the pattern to be placed on the mask contains many identical subpatterns as does the pattern for a typical semiconduct memory or logic circuit, this repetitiousness cannot be utilized unless the subpatterns have the same 256.times.256 um dimensions as the cells formed by the movement of the electron beam.
It takes a long time to develop the correct exposure pattern data for a large mask if there is no repetitive pattern in the pattern which corresponds to the cell size. The time required for this data development is longer than the time required for the apparatus to expose the entire mask. This means that the known apparatus cannot be used with a high efficiency. Further, since all the data representing identical subpatterns must be individually stored unless the subpatterns have the same size and location as a corresponding cell, the electron beam apparatus must have the capacity for storing a large amount of exposure pattern data.